Electromagnetic waves and signals (hereinafter “signals”) are utilized for many different purposes. For example, electromagnetic signals may be processed in order to convey information, such as by attenuating and/or amplifying electromagnetic wave characteristics, for instance, as is seen when modulating the amplitude, frequency or phase of an electrical current or radio frequency (RF) wave to transmit data. As another example, power may be conveyed along a wave in a controlled fashion by attenuating and or amplifying electromagnetic signals, such as is seen when modulating voltage or current in a circuit. Moreover, the uses may be combined, such as when information may be conveyed through a signal by processing power characteristics.
Electromagnetic signal processing may be accomplished through digital or analog techniques. Digital and analog attenuation and/or amplification also may be combined—that is, the same wave form may be subject to various types of digital and/or analog attenuation and/or amplification within a system in order to accomplish desired tasks.
Frequency hopping spread spectrum (“FHSS”) is a method of transmitting electromagnetic signals by rapidly switching the carrier among many different frequencies. In a frequency hopping scheme, each successive communication frame is transmitted on a different frequency according to a pseudorandom sequencing code known by both the transmitter and the receiver. FHSS communications offer several advantages compared to communications on a single carrier frequency. For example, FHSS signals are both difficult to intercept and highly resistant to noise and interference. In addition, because FHSS signals are resistant to interference, many different FHSS communications can share the same frequency band with minimal interference. In a multi-user environment, this allows for more efficient use of bandwidth.
Frequency hopping spread spectrum technology is used in certain military wireless communication systems to avoid intentional jamming by hostile transmitters. Frequency hopping also can be found in certain civilian applications, such as the GSM wireless communication standard.
Conventional FHSS communication systems have involved the use of phase-locked loop systems, also known as phase-locked loops. In the processing of electronic signals, phase-locked loops may be used for a wide variety of purposes, such as frequency synthesizers and phase modulators in transceivers for wireless communications devices such as GSM (Global System for Mobile communications), PCS (Personal Communication System), PCN (Personal Communications Network), and DECT (Digital Enhanced Cordless Telecommunications) devices. In a typical phase-locked loop (“PLL”), a reference signal at a reference frequency is input to a phase/frequency detector along with a feedback signal derived from the output of the PLL. The output of the frequency/phase detector is filtered by a loop filter and applied to a voltage controlled oscillator (“VCO”) to generate an output signal at the desired frequency. The output signal frequency then forms at least part of the feedback signal input to the phase/frequency detector.
Traditionally, frequency hoppers could achieve small frequency hops by changing the voltage bias on a VCO. However, large frequency hops can be difficult to achieve in this manner. Instead, conventional frequency hoppers have achieved large frequency hops by switching between multiple PLLs, where each PLL is tuned to a certain central frequency that matches one of the hopping choices.
The conventional approach of frequency hopping using multiple PLLs has several disadvantages. For example, the requirement of multiple PLLs complicates the circuitry of the frequency hopper. In addition, to hop in a timely manner and achieve an acceptable waveform quality, the PLLs must be designed such that they can lock into the required frequency in a very short period of time. Another disadvantage of a multiple-PLL frequency-hopper is that it requires fast switches.
Accordingly, there is a need for methods and systems for frequency-hopping that allow for fast, large frequency hops without the need for multiple PLLs or fast switches. There also is a need for a frequency hopper that is less dependent on the ability of a PLL to lock into a required frequency in a very short period of time.